feat: add 'methodNotAllowed' handler for '405 Method Not Allowed' responses

src/hono-base.ts

@@ -17,6 +17,7 @@ import type {
   HandlerInterface,
   MergePath,
   MergeSchemaPath,
+  MethodNotAllowedHandler,
   MiddlewareHandler,
   MiddlewareHandlerInterface,
   Next,
@@ -179,11 +180,14 @@ class Hono<
     })
     clone.errorHandler = this.errorHandler
     clone.#notFoundHandler = this.#notFoundHandler
+    clone.#methodNotAllowedHandler = this.#methodNotAllowedHandler
     clone.routes = this.routes
     return clone
   }
 
   #notFoundHandler: NotFoundHandler = notFoundHandler
+  #methodNotAllowedHandler: MethodNotAllowedHandler | null = null
+
   // Cannot use `#` because it requires visibility at JavaScript runtime.
   private errorHandler: ErrorHandler = errorHandler
 
@@ -293,6 +297,28 @@ class Hono<
     return this
   }
 
+  /**
+   * `.methodNotAllowed()` allows you to customize a Method Not Allowed Response.
+   *
+   * @see {@link https://hono.dev/docs/api/hono#method-not-allowed}
+   *
+   * @param {MethodNotAllowedHandler} handler - request handler for method-not-allowed
+   * @returns {Hono} changed Hono instance
+   *
+   * @example
+   * ```ts
+   * app.methodNotAllowed((c, allowedMethods) => {
+   *   return c.text(`Method not allowed. Allowed: ${allowedMethods.join(', ')}`, 405, {
+   *     Allow: allowedMethods.join(', ').toUpperCase()
+   *   })
+   * })
+   * ```
+   */
+  methodNotAllowed = (handler: MethodNotAllowedHandler<E>): Hono<E, S, BasePath, CurrentPath> => {
+    this.#methodNotAllowedHandler = handler
+    return this
+  }
+
   /**
    * `.mount()` allows you to mount applications built with other frameworks into your Hono application.
    *
@@ -390,6 +416,24 @@ class Hono<
     this.routes.push(r)
   }
 
+  #findAllowedMethods(path: string): string[] {
+    const allowedMethods = new Set<string>()
+    const allMethods = METHODS.map((m) => m.toUpperCase())
+
+    for (const method of allMethods) {
+      const matchResult = this.router.match(method, path)
+      // Check if there are any method-specific routes (excluding METHOD_NAME_ALL middleware)
+      const hasMethodSpecificRoute = matchResult[0].some(
+        (match: [[H, RouterRoute], unknown]) => match[0][1].method !== METHOD_NAME_ALL
+      )
+      if (hasMethodSpecificRoute) {
+        allowedMethods.add(method)
+      }
+    }
+
+    return Array.from(allowedMethods)
+  }
+
   #handleError(err: unknown, c: Context<E>): Response | Promise<Response> {
     if (err instanceof Error) {
       return this.errorHandler(err, c)
@@ -420,6 +464,19 @@ class Hono<
       notFoundHandler: this.#notFoundHandler,
     })
 
+    // Check if there are any method-specific routes (excluding METHOD_NAME_ALL middleware)
+    const hasMethodSpecificRoute = matchResult[0].some(
+      (match: [[H, RouterRoute], unknown]) => match[0][1].method !== METHOD_NAME_ALL
+    )
+
+    // Check for method not allowed if no method-specific match found and handler is set
+    if (!hasMethodSpecificRoute && this.#methodNotAllowedHandler) {
+      const allowedMethods = this.#findAllowedMethods(path)
+      if (allowedMethods.length > 0) {
+        return this.#methodNotAllowedHandler(c, allowedMethods)
+      }
+    }
+
     // Do not `compose` if it has only one handler
     if (matchResult[0].length === 1) {
       let res: ReturnType<H>

src/hono.test.ts

@@ -1340,6 +1340,200 @@ describe('Not Found', () => {
   })
 })
 
+describe('Method Not Allowed', () => {
+  it('Should return 404 by default when method is not allowed', async () => {
+    const app = new Hono()
+
+    app.get('/hello', (c) => {
+      return c.text('hello')
+    })
+
+    const res = await app.request('http://localhost/hello', { method: 'POST' })
+    expect(res.status).toBe(404)
+    expect(await res.text()).toBe('404 Not Found')
+  })
+
+  it('Should return 405 when methodNotAllowed handler is set', async () => {
+    const app = new Hono()
+
+    app.get('/hello', (c) => {
+      return c.text('hello')
+    })
+
+    app.methodNotAllowed((c, allowedMethods) => {
+      return c.text('405 Method Not Allowed', 405, {
+        Allow: allowedMethods.join(', ').toUpperCase(),
+      })
+    })
+
+    const res = await app.request('http://localhost/hello', { method: 'POST' })
+    expect(res.status).toBe(405)
+    expect(res.headers.get('Allow')).toBe('GET')
+    expect(await res.text()).toBe('405 Method Not Allowed')
+  })
+
+  it('Should return 404 when path does not exist even with methodNotAllowed handler', async () => {
+    const app = new Hono()
+
+    app.get('/hello', (c) => {
+      return c.text('hello')
+    })
+
+    app.methodNotAllowed((c, allowedMethods) => {
+      return c.text('405 Method Not Allowed', 405, {
+        Allow: allowedMethods.join(', ').toUpperCase(),
+      })
+    })
+
+    const res = await app.request('http://localhost/nonexistent', { method: 'POST' })
+    expect(res.status).toBe(404)
+    expect(await res.text()).toBe('404 Not Found')
+  })
+
+  it('Should include all allowed methods in Allow header', async () => {
+    const app = new Hono()
+
+    app.get('/hello', (c) => c.text('GET'))
+    app.post('/hello', (c) => c.text('POST'))
+    app.put('/hello', (c) => c.text('PUT'))
+
+    app.methodNotAllowed((c, allowedMethods) => {
+      return c.text('405 Method Not Allowed', 405, {
+        Allow: allowedMethods.join(', ').toUpperCase(),
+      })
+    })
+
+    const res = await app.request('http://localhost/hello', { method: 'DELETE' })
+    expect(res.status).toBe(405)
+    const allowHeader = res.headers.get('Allow')
+    expect(allowHeader).toContain('GET')
+    expect(allowHeader).toContain('POST')
+    expect(allowHeader).toContain('PUT')
+    expect(allowHeader?.split(', ').length).toBe(3)
+  })
+
+  it('Should work with custom methodNotAllowed handler', async () => {
+    const app = new Hono()
+
+    app.get('/hello', (c) => c.text('hello'))
+
+    app.methodNotAllowed((c, allowedMethods) => {
+      return c.json({ error: 'Method not allowed', allowed: allowedMethods }, 405, {
+        Allow: allowedMethods.join(', ').toUpperCase(),
+      })
+    })
+
+    const res = await app.request('http://localhost/hello', { method: 'POST' })
+    expect(res.status).toBe(405)
+    expect(res.headers.get('Allow')).toBe('GET')
+    const json = await res.json()
+    expect(json.error).toBe('Method not allowed')
+    expect(json.allowed).toEqual(['GET'])
+  })
+
+  it('Should work with routes with parameters', async () => {
+    const app = new Hono()
+
+    app.get('/user/:id', (c) => {
+      return c.text(`User ${c.req.param('id')}`)
+    })
+
+    app.methodNotAllowed((c, allowedMethods) => {
+      return c.text('405 Method Not Allowed', 405, {
+        Allow: allowedMethods.join(', ').toUpperCase(),
+      })
+    })
+
+    const res = await app.request('http://localhost/user/123', { method: 'POST' })
+    expect(res.status).toBe(405)
+    expect(res.headers.get('Allow')).toBe('GET')
+  })
+
+  it('Should work with HEAD method (which maps to GET)', async () => {
+    const app = new Hono()
+
+    app.get('/hello', (c) => c.text('hello'))
+
+    app.methodNotAllowed((c, allowedMethods) => {
+      return c.text('405 Method Not Allowed', 405, {
+        Allow: allowedMethods.join(', ').toUpperCase(),
+      })
+    })
+
+    // HEAD should work (maps to GET)
+    const headRes = await app.request('http://localhost/hello', { method: 'HEAD' })
+    expect(headRes.status).toBe(200)
+
+    // But POST should return 405
+    const postRes = await app.request('http://localhost/hello', { method: 'POST' })
+    expect(postRes.status).toBe(405)
+    expect(postRes.headers.get('Allow')).toBe('GET')
+  })
+
+  it('Should work with app.route()', async () => {
+    const app = new Hono()
+    const subApp = new Hono()
+
+    subApp.get('/hello', (c) => c.text('hello'))
+    app.route('/api', subApp)
+
+    app.methodNotAllowed((c, allowedMethods) => {
+      return c.text('405 Method Not Allowed', 405, {
+        Allow: allowedMethods.join(', ').toUpperCase(),
+      })
+    })
+
+    const res = await app.request('http://localhost/api/hello', { method: 'POST' })
+    expect(res.status).toBe(405)
+    expect(res.headers.get('Allow')).toBe('GET')
+  })
+
+  it('Should work with multiple methods on same path', async () => {
+    const app = new Hono()
+
+    app.get('/resource', (c) => c.text('GET'))
+    app.post('/resource', (c) => c.text('POST'))
+    app.delete('/resource', (c) => c.text('DELETE'))
+
+    app.methodNotAllowed((c, allowedMethods) => {
+      return c.text('405 Method Not Allowed', 405, {
+        Allow: allowedMethods.join(', ').toUpperCase(),
+      })
+    })
+
+    const res = await app.request('http://localhost/resource', { method: 'PUT' })
+    expect(res.status).toBe(405)
+    const allowHeader = res.headers.get('Allow')
+    expect(allowHeader).toContain('GET')
+    expect(allowHeader).toContain('POST')
+    expect(allowHeader).toContain('DELETE')
+  })
+
+  it('Should work with app.use() middleware', async () => {
+    const app = new Hono()
+
+    app.methodNotAllowed((c, allowedMethods) => {
+      return c.text(`Method not allowed. Allowed: ${allowedMethods.join(', ')}`, 405, {
+        Allow: allowedMethods.join(', ').toUpperCase(),
+      })
+    })
+
+    // Adding middleware should not prevent methodNotAllowed from being called
+    app.use(async (c, next) => {
+      await next()
+    })
+
+    app.get('/', (c) => {
+      return new Response('Hello, World!')
+    })
+
+    const res = await app.request('http://localhost/', { method: 'POST' })
+    expect(res.status).toBe(405)
+    expect(res.headers.get('Allow')).toBe('GET')
+    expect(await res.text()).toBe('Method not allowed. Allowed: GET')
+  })
+})
+
 describe('Redirect', () => {
   const app = new Hono()
   app.get('/redirect', (c) => {

src/index.ts

@@ -24,6 +24,8 @@ export type {
   ErrorHandler,
   Handler,
   MiddlewareHandler,
+  MethodNotAllowedHandler,
+  MethodNotAllowedResponse,
   Next,
   NotFoundResponse,
   NotFoundHandler,

src/types.ts

@@ -111,6 +111,23 @@ export type NotFoundHandler<E extends Env = any> = (
   ? NotFoundResponse | Promise<NotFoundResponse>
   : Response | Promise<Response>
 
+/**
+ * You can extend this interface to define a custom `c.methodNotAllowed()` Response type.
+ *
+ * @example
+ * declare module 'hono' {
+ *   interface MethodNotAllowedResponse extends Response, TypedResponse<string, 405, 'text'> {}
+ * }
+ */
+export interface MethodNotAllowedResponse {}
+
+export type MethodNotAllowedHandler<E extends Env = any> = (
+  c: Context<E>,
+  allowedMethods: string[]
+) => MethodNotAllowedResponse extends Response
+  ? MethodNotAllowedResponse | Promise<MethodNotAllowedResponse>
+  : Response | Promise<Response>
+
 export interface HTTPResponseError extends Error {
   getResponse: () => Response
 }